Process for preparing products from legumes using centrifugation

ABSTRACT

A process for preparing products from legumes which comprises preparing an aqueous suspension containing finely ground seed from peas or beans, at a pH within the range of about 2.0 to 10.0, subjecting the suspension to one or more centrifugation operations and isolating therefrom at least one product containing essentially the protein content of the seed and another product containing essentially the starch content of the seed. A good quality fibrous by-product may also be isolated. The products are useful in the food industry.

This invention relates to a process for preparing products from legumesand more particularly it relates to a process for the separation of oneor more protein products and one or more carbohydrate products fromlegumes such as peas and beans. These protein and carbohydrate productsare useful in the food processing industry, for example as additives tofood preparations, or in other industries such as the paper industry andthe pharmaceutical industry. A useful by-product of the process is goodquality fibrous material which can be used in the food processingindustry.

It is known that dry legumes such as dry field peas, faba beans andwhite pea beans have a protein content ranging from about 21% to about31% and a starch or carbohydrate content ranging from about 43% to about53%. It is often desirable to separate the protein content from thestarch content in such legumes, as far as is possible, in order toprovide a protein product relatively high in protein content and astarch product which is relatively low in undesired impurities.

It has now been found that by operating the process of the presentinvention, it is possible to separate essentially the protein contentfrom the starch or carbohydrate content of legumes such as peas andbeans, and thus prepare protein products and starch products. Duringoperation of this process, the desired products are prepared underconditions such that enzymatic activity is substantially inhibited, oris maintained at a relatively low level, thereby minimizing thedevelopment of odour or flavour in the prepared products.

The invention as claimed herein is a process for the preparation of anovel protein product or a novel starch product from legume seed whichcomprises suspending finely ground or powdered legume seed in an aqueousmedium to provide an aqueous suspension wherein the pH is within therange of from about 2.0 to about 10.0, subjecting said aqueoussuspension to centrifugation to provide an overflow fraction containinga major proportion of proteins and an underflow fraction containing amajor proportion of starches, and thereafter adjusting the pH of saidoverflow fraction and isolating therefrom a protein product, oradjusting the pH of said underflow fraction and isolating therefrom astarch product.

The legume seed used as starting material for the above process may bepeas or beans, or a mixture of said peas and beans. A preferred startingmaterial is yellow field peas and suitable varieties of peas areTrapper, Century, Flavo, Victoria and First & Best, while suitablevarieties of beans are Diana and Ackerperle.

The starting material in the form of an aqueous suspension containingfinely ground or powdered legume seed may be prepared in any mannersuitable for, or convenient for, the handling of such legume seed. Thus,for example, the seed, which may or may not have been subjected to apreliminary treatment to reduce the moisture content thereof, may befinely ground, in the dry state, by the use of dry milling equipment.The powder or flour so obtained may then be suspended in an aqueousmedium at the appropriate pH to provide the required aqueous suspension.

The peas and beans used to provide powdered starting material aregenerally received with hulls intact, sometimes associated with fieldchaff or other unwanted products from the area where they are grown.These peas and beans usually have a moisture content of about 14% to 16%and they may be cleaned in the usual cleaning equipment and optionallydried at the same time to reduce the moisture content to a figure ofabout 10% to facilitate the removal of the hulls by means of suitabledehulling equipment, for example commercially available equipmentincorporating discs or rollers. At this point, the starting materialbeing prepared is in the form of clean, dehulled seed, optionally havinga reduced moisture content, which contains as its major components,starches, proteins, sugars and a certain amount of fibre.

The clean, dehulled seeds are then ground into a powder or flour andsuch grinding may be carried out by a dry milling procedure, for exampleusing a high energy mill, to produce a flour which will permitrelatively easy dispersion in water. A flour having a particle size nogreater than about 120 microns is generally satisfactory for use in theprocess of the present invention.

The powder or flour from the ground seed may be suspended in achemically treated aqueous medium at ambient temperature, for example atabout 15° C. to 25° C., and the ratio of water to flour may convenientlybe from about 3:1 to about 10:1 by weight. The aqueous medium maycontain an acid or an alkali, or an appropriate salt thereof, in orderto provide a pH within the desired range of about 2.0 to about 10.0. Theaqueous medium may contain, for example, hydrochloric acid, phosphoricacid or sodium hydroxide. The aqueous suspension so obtained, in theform of a fine aqueous dispersion or slurry, is preferably rapidlystirred or agitated during the thorough mixing to provide a suspensionhaving a pH within the range of about 2.0 to about 10.0 using an acid oran alkali or an alkaline salt, as the case may be, according to the pHrequired. An alkaline salt used to achieve the desired pH of the aqueoussuspension may be, for example, sodium pyrophosphate, sodiumtrimetaphosphate, sodium tripolyphosphate, sodium tetrametaphosphate orsodium bisulphite.

It is preferred that the pH of the aqueous suspension be within therange of about 2.2 to about 3.2 and more particularly within the rangeof about 2.5 to 3.0. This may be achieved by the addition of an acidsuch as hydrochloric acid. It is preferred that the water bepreacidified prior to the introduction of the legume powder or flour sothat the flour is thus added to an acidulated aqueous medium in order toensure proper mixing and distribution of the flour throughout theaqueous slurry, thereby avoiding local concentration of acid which maydegradate or affect the proteins present in the flour. A pH lower thatabout 3.0 is preferred because operation of the process at such a lowerpH is associated with relatively low enzymatic activity and thereforereduced odor or flavour development in the products isolated duringsubsequent processing. Operation of the process at low pH levels, forexample at a pH of about 2.5 to 3.0, provides a method of controllingand minimizing the development of characteristic off-flavours, generallyreferred to or described as "beaniness" , in the protein isolate productobtained from the process. Adequate stirring or mixing at this initialstage may be brought about by the use of continuous in line mixingdevices or equipment. By operation at this relatively low pH of about2.5 to 3.0, it is generally found that about 50% by weight of theproteins present in the original flour may be in solution in the aqueoussuspension. It is to be understood that by operating at higher pHranges, for example in the range of pH about 6.5-9.5, the amount ofprotein in solution in the aqueous suspension tends to vary according tothe means and conditions used to obtain and maintain the pH of theaqueous suspension. Increasing the pH of the suspension tends toincrease enzymatic activity thus leading to certain flavour or odourdevelopment. The process may nevertheless be operated at such high pHranges where such flavour or odour development is not unacceptable inthe protein products isolated from the process.

It will be appreciated that the aqueous suspension containing legumeseed in a finely divided state, to be used as starting material, mayalternatively, be obtained by means of a wet grinding procedure wherebythe seed is ground in an aqueous medium containing acid or an alkali, ora salt thereof, to provide the desired pH of the aqueous suspension. Thewet grinding procedure may be carried out in any kind of wet grindingequipment, for example in a Bauer type plate grinder, in an aqueousmedium, such as acidulated water containing hydrochloric acid, wherebyan aqueous suspension is obtained containing finely divided legume seedin the form of an aqueous slurry at the desired pH for subsequentprocessing.

The aqueous suspension obtained from the dry milling procedure or thewet grinding procedure at the desired pH is in the form of an aqueousslurry or fine dispersion which may be screened or filtered at one ormore stages of the processing operation in order to remove fibrousmaterial. If the aqueous slurry has been produced by means of a wetgrinding procedure, for example using yellow field pea seed (split peas)in an acidulated aqueous medium containing hydrochloric acid, thesolution may first be screened to remove as much as possible of thefibrous material. Such screening may be carried out by passage of theaqueous slurry through a suitable screening device such as a vibratoryscreen, filter press, a rotary vacuum filter, a centrifugal separator oran ultrafiltration membrane. The former filter and screens, the lattermembrane may retain some starches and fibrous material while otherstarches and proteins pass through and the fibrous material cansubsequently be separated from the starches.

The screened aqueous suspension, as a slurry or fine dispersion,containing a substantial proportion of proteins in solution, is thensubjected to centrifugal action to separate the mixture into a so-calledliquid fraction and a solid fraction. A suitable decanter or horizontaltype centrifuge, such as a Sharples Pennwalt Series P super decantercentrifuge, or a series of hydroclones, such as a Dorr Oliverhydroclone, may be used. As a result of this centrifugal action, thereis obtained a low solids content overflow portion, a so-called liquidfraction, containing essentially soluble proteins with some sugars, anda high solids content underflow portion, a so-called solid fraction,containing essentially insoluble starches with some insoluble proteins,and fibrous material.

The said overflow portion or liquid fraction containing essentialsoluble proteins with some sugars may then be further treated in orderto obtain therefrom the desired proteins. If this liquid fractioncontains an appreciable amount of insoluble solid material, it may beadvantageous to subject it to an additional centrifugation operation inorder to remove a solid underflow portion containing solids, such asfibrous material, degraded starches and solid proteins, while providingan overflow liquid fraction rich in dissolved proteins. If the liquidfraction, with or without additional centrifugation, is at a relativelylow pH, preferably within the range of about 2.0 to about 3.0 andespecially within the range of about 2.5 to about 3.0, it is generallyadvisable to increase the pH thereof to a figure of between about 4.4 to4.6. If the liquid fraction is, however, already at a high pH, forexample at a pH of about 8.5 to about 9.5, it will be necessary to lowerthe pH thereof to a figure of between about 4.4 to 4.6. This figure isknown as the isoelectric point for proteins and it is the point where amajority of the proteins coagulate and are precipitated from solution.Any adjustment of pH may be carried out by the addition of a diluteaqueous solution of an acid, such as hydrochloric acid, or an alkali,such as sodium hydroxide. The proteins are thereby coagulated and beginto precipitate. The solid protein so obtained may be removed from thesoluble sugars remaining in solution by use of a suitable centrifuge,such as a desludging type of centrifuge commercially available as aWestphalia or DeLaval centrifuge. The solid fraction in the form of asludge containing solid proteins so isolated may, if desired, be furthertreated by dispersing the sludge in about 3 to 5 parts of water to forman aqueous slurry and thereafter adding acid, for example hydrochloricacid, as necessary, to maintain an aqueous slurry of about pH 4.4 to4.6. The slurry is again centrifuged to obtain a solid fraction which isessentia1ly proteins substantially free from sugars and relatively freefrom odour and flavour.

The high solids content underflow portion, the so-called solid fraction,containing essentially insoluble starches with some insoluble proteins,mentioned above, may be further treated in order to separate thestarches from the remaining proteins and thus obtain a starch product.This solid fraction may conveniently be slurried in pretreated water toprovide an aqueous slurry having a pH within the range of about 8.5 toabout 9.5. The pretreated water may contain an alkali such as sodiumhydroxide. The adjustment in pH is generally sufficient to bring aboutsolubilization of the remaining proteins such that the aqueous alkalineslurry now consists of a solid phase containing essentially starches anda liquid phase containing essentially proteins. This aqueous slurry mayconveniently be separated by centrifugation using a centrifuge such asthat referred to above as a decanter or horizontal type of centrifuge,available as a Sharples Pennwalt Series P super decanter centrifuge, ora series of hydroclones, such as a Dorr Oliver hydroclone. Suchseparation provides a liquid fraction containing essentially solubleproteins and a solid fraction containing essentially insoluble starcheswith possibly small amounts, of the order of about 1% to about 1.5% ofproteins. This solid fraction may be retreated by further slurrying inwater with adjustment of the pH of the aqueous slurry to within therange of about 4 to about 7, separating and washing to provide a solidfraction which is essentially starches with relatively little proteinpresent, the protein content being down as low as 0.5%.

The liquid fraction or fractions from this separation procedure containsessentially soluble proteins and any insoluble solid material thereinmay be removed by means of an additional centrifugation operation toseparate fibrous material, degraded starches or insoluble proteins. Theliquid fraction thus remaining is generally at a pH within the range ofabout 8.0 to about 9.5 and therefore requires adjustment of the pH to afigure of about 4.4 to 4.6 (isoelectric point) in order to coagulate andprecipitate proteins. This may be achieved by the addition of an acid,such a hydrochloric acid, in order to adjust the liquid fraction to a pHof about 4.4 to 4.6. At this point, the proteins coagulate andprecipitate into a solid form. This solid form of proteins mayconveniently be separated from the remaining soluble sugars bysub3ecting the mixture to centrifugation, for example by use of adesluding type of centrifuge commercially available as a Westphalia orDeLaval centrifuge. The solid protein portion thus obtained can beretreated, if desired, by reslurrying in 3-5 parts water with adjustmentof the pH again to a figure of about 4.4 to 4.6. After furthercentrifugation, the solid protein product so obtained consistsessentially of proteins with little or no sugars and is relatively freefrom odour or flavour.

The two protein products obtained from the process described above maybe dried independently or they may be combined and dried as a singleprotein product. If dried separately, the first protein product has avery low flavour and when dried in a spray type dryer at lowtemperature, it provides a protein powder which is extremely soluble inwater. The second protein product, when dried in a spray type dryer atlow temperature, provides a second protein powder characterized by highwater absorption and oil emulsification properties.

Alternatively, the two protein fractions, in the form of their so-calledliquid protein fractions, may be combined into a single liquid proteinfraction which can then be adjusted to a pH of about 4.4 to 4.6, (theisoelectric point), and the proteins thereby coagulate and precipitate.This combined protein product can then be separated and retreated, asdescribed above, by slurrying in water with adjustment of the pH toabout 4.4 to 4.6 followed by centrifugation. The solid protein fractioncan be spray dried at low temperature to provide a protein powdercontaining a high content of proteins.

It has been found that the final dried protein product powder generallyhas a moisture content in the range of about 4% to about 7% while thefinal dried starch product powder generally has a moisture content inthe range of about 7% to about 13%.

The invention is illustrated by, but not limited by, the followingExamples:

EXAMPLE 1

Dehulled dry yellow field peas seeds (Variety: Century) having amoisture content of about 7% by weight are dry milled in an Alpine pinmill until a pea flour or powder is obtained having a particle sizewithin the range of about 80 to 120 mesh, the flour being able to passconveniently through a sieve of 100 mesh. This flour (20 kg) issuspended in acidulated water, made up from 79.7 kg of water and 1.25 kgof hydrochloric acid (31.45% HCl, by adding the flour portionwise to thetotal amount of acidulated water. The aqueous suspension or slurry soobtained is vigorously agitated and the pH of the final slurry is about2.5 with a substantial proportion of the proteins in the pea flourhaving been solublized.

The aqueous slurry is then pumped into a decanter or horizontal typecentrifuge, (available commercially, for example, as a Sharples PennwaltSeries P super decanter) and is subjected to centrifugation. There isthus obtained a liquid overflow Fraction 1 (5-85 kg) containingessentially soluble proteins together with some soluble sugars and somefibrous matter, and a solid underflow Fraction 2 (19-23 kg) containingessentially starch with some insoluble proteins. The said liquidFraction 1 has a dry solids content of 6-8.5 kg and, of this, theprotein proportion amounts to 4-5.2 kg. The said solid Fraction 2 has adry solids content of 8-13 kg and, of this, the protein proportionamounts to 0.4 to 0.8 kg, the remainder being essentially starches.

The liquid overflow Fraction 1, at a pH of about 2.5, is subjected to afurther centrifugation stage (DeLaval BRPX type desludger centrifuge) inorder to separate essentially the solid fibrous matter from the proteinsand sugars. There is thus obtained a liquid overflow Fraction 3 (48-58kg) and a solid underflow Fraction 4 (24-30 kg). The said Fraction 3 hasa dry solids content of 3.5 to 4.5 kg, and of this, the proteinproportion amounts to 2.5-3.3 kg. The said solid Fraction 4 has a drysolids content of 4-5 kg and of this, the protein proportion amounts to1.3-2 kg.

The said liquid Fraction 3 is then agitated and adjusted to theisoelectric point (pH about 4.4 to 4.6) by the addition of 3N aqueoussodium hydroxide. The milky appearance of the mixture indicatescoagulation and precipitation of solid proteins while sugars remainsubstantially in solution. The mixture is separated into liquid andsolid Fractions by passing it through a de-sludging type of centrifuge,commercially available as a Westphalia SB80 or DeLaval BRPX 417centrifuge. There is thus obtained a liquid overflow Fraction 5 (27-33kg) and a solid underflow Fraction 6 (18020 kg). This liquid Fraction 5has a dry solids content of 0.85-1.4 kg and, of this, the proteinproportion amounts to only 0.2-0.55 kg. The solid Fraction 6 containsessentially solid proteins and has a dry solids content of 2.8-3 kg and,of this, the protein proportion amounts to 2.2-2.5 kg.

The liquid overflow Fraction 5 contains soluble protein and solublesugars. It is subjected to an ultrafiltration treatment in order tofurther separate a portion of protein from the sugars. Suitableultrafiltration equipment, such as a Dorr Oliver type of machine havingmembranes with a molecular weight cut-off of about 24,000 is used toretain additional protein on the membranes thereby removing it from thedissolved sugars. This protein so retained can be added to other proteinfractions and further processed.

The solid Fraction 6 is further treated, to remove possibleoff-flavoured sugars, by suspending it in 50 kg of water to obtain anaqueous slurry which is then acidified carefull with hydrochloric acidin order to maintain the slurry at pH 4.5. The mixture is againsubjected to centrifugation to provide a liquid overflow Fraction 7(28-32 kg) and a solid underflow Fraction 8 (14-18 kg) as a cake ofsolid proteins. This cake is then adjusted to a pH of between 4.5 and7.5 with 5N sodium hydroxide and it is then dried in a spray type dryersuch as a DeLaval type dryer at a low inlet temperature (about 330°-425°F.) to minimize any risk of heat denaturation of the proteins. There isthus obtained a dry powder, containing a high concentration of proteins,which has little noticeable odour or flavour. This protein powdercontains about 88-93% of proteins and is characterized by having highsolubility at low and neutral pH aqueous conditions. This protein powdercontains about 4-7% of moisture.

The solid underflow Fraction 2, mentioned above, is reslurried with 3-5parts (40 kg) of water containing sodium hydroxide such that the aqueousslurry so obtained has a pH of about 8.5-9.5 in order to solubilize theproteins present. This slurry at pH 8.5 to 9.5 is then separated bymeans of a decanter or horizontal type centrifuge (Sharples PennwaltSeries P super decanter centrifuge) to provide a liquid overflowFraction 9 (37-41 kg) containing essentially proteins and a solidunderflow Fraction 10 (20-24 kg) containing essentially starches withabout 1.5% soluble proteins.

The said solid Fraction 10 is combined with two parts of water (40-48Kg) and the pH is adjusted to 7 by the addition of hydrochloric acid.The aqueous mixture is then subjected to centrifugation (liquid cyclonessuch as Dorr Clones or Bauer type liquid cyclones). There is thusobtained a liquid overflow Fraction 17 which may be discarded oralternately, because of its low solids content, may be used as make upwater at some other stage in the process. The solid underflow Fraction18 is dried in a spray type dryer to produce a starch product powderwhich is high in starch content, having a starch content ofapproximately 98% on a dry weight basis and containing approximately 0.3to 0.7% protein and characterized by its pure white starch nature. Thestarch powder contains approximately 7% to 13% of moisture. Alternately,solid Fraction 18 may be dewatered in a centrifuge such as a DeLavaldecanter type or solid Fraction 18 may be dewatered by the use of arotary vacuum filter. The resulting cake has a solid content ofapproximately 50-55%. This cake may then be dried in a dispersion typedryer or alternately on a mixture is centrifuged by use of a DeLavaltype BRPX Desludger Centrifuge thereby providing a liquid overflowFraction 13 (0-35 kg), having a relatively low dry solids content of0.4-0.8 kg of which only 0.04-0.1 kg is protein, and a solid underflowFraction 14 (11-13 kg), having a dry solids content of 1.5-2 kg which isessentially proteins, the proportion of the latter amounting to 1.3-1.6kg.

The liquid Fraction 13, like Fraction 5 mentioned above, containssoluble proteins together with soluble sugars, and may be subjected toan ultrafiltration treatment using a Dorr Oliver type of ultrafiltrationunit having membranes with a molecular weight cut-off of about 24,000.The membranes thereby retain a certain proportion of the solubleproteins while the soluble sugars pass through the membranes. Theadditional protein so retained can be added to other protein fractionsand further processed.

The solid Fraction 14 containing essentially proteins is furthertreated, to improve the content of proteins therein, by resuspending itin 3-5 parts of water (37 kg) while maintaining the pH of the aqueousmixture at a figure of about 4.4 to 4.6. The aqueous suspension issubjected to centrifugation and there is thus obtained a liquid overflowFraction 15 (36-42 kg), having a low dry solids content of 0.2-0.35 kgof which the protein proportion is only 0.04-0.08 kg; and a solidunderflow Fraction 16 (9.5-1.2 kg). The latter Fraction 16 has a drysolids content of 1.4-1.8 kg which is essentially proteins (1.3-1.6 kg).This Fraction 16 is adjusted to a pH between about 4.5 and 7.5 withaqueous sodium hydroxide and it is then dried in a spray type dryer,such as a DeLaval type dryer at a low inlet temperature (about 330°-425°F.). There is thus obtained a dry powder, containing a highconcentration of proteins, which has little or no noticeable odour orflavour. This concentrated protein powder differs from the powderobtained from Fraction 8 in that it has a lower solubility index, higherwater absorption and a greater degree of heat coagulability than thepowder prepared from Fraction 8.

EXAMPLE 2

The procedure described in Example 1 for the preparation of pea flourusing yellow field peas (Century variety) was repeated. An aqueousslurry was then prepared using the pea flour (25 kg), water (99.6 kg)and hydrochloric acid (1.6 kg), the latter being commercial gradehydrochloric acid (20° Be: 31.45% HCl).

The aqueous slurry is then pumped to a screening stage where the bulk ofthe fibrous material is removed without losing any appreciable quantityof the proteins and starches, either in solution or in suspension. Thisgenerally is achieved by using a suitable screen size dependent upon therelative particle size of the original flour and the particle size ofthe fibrous material. Generally a screen size of about 100 microns isappropriate and a suitable screening device operated under pressure suchas a Dorr Oliver DSM Screen, removes the fibrous material and thusleaves an aqueous slurry containing substantially all of the protein andstarches from the pea seeds.

Following the procedure described in Example 1 , the firstcentrifugation procedure using a decanter or nozzle type centrifugeprovides a liquid overflow Fraction 1 (96.5-101 kg), which isessentially proteins, having a dry solids content of 8.5-10 kg of whichthe proportion of proteins present therein is 5.5-6.3 kg, and a solidunderflow Fraction 2 (24-28 kg), which is essentially starches with asmall amount of proteins. Solid Fraction 2 has a dry solids content of13.5-15 kg of which only 0.5-0.9 kg is protein.

The liquid Fraction 1 at pH 3 is subjected to further centrifugationusing a desludger type centrifuge. Thus is thereby obtained a liquidoverflow Fraction 3 (61-69 kg) having a dry solids content of 5.1-5.9 kgof which 3.4-4.0 is protein, together with a solid underflow Fraction 4(30-37 kg), having a dry solids content of 4.8-5.4 kg of which 1.8-2.2is protein.

Likewise, the solid Fraction 2 is treated in a similar manner to thatdescribed in Example 1. It is reslurried in water (26.9 kg) and themixture is adjusted to a pH of about 8.5 by 10 the addition of sodiumhydroxide. By means of a decanter or horizontal type centrifuge, it isseparated further into starches and proteins. There is thus obtained aliquid overflow Fraction 5 (47.4-54.4 kg) having a dry solids content of3.8-4.3 of which 2.1-2.8 kg is protein, and a solid underflow Fraction 6(22-29 kg) having a dry solids content of 10.2-11 kg of which only0.06-0.09 kg is protein.

The solid Fraction 4 and the liquid Fraction 5, both of which containprotein, are combined and the pH of the aqueous mixture is adjusted to afigure of about 8.5 by the addition of aqueous sodium hydroxide. Themixture so adjusted is subjected to centrifugation (DeLaval type) andthere is thereby obtained a liquid overflow Fraction 7 (64.2-78.4 kg),having a dry solids content of 2.5-3.4 kg of which the proteinproportion amounts to 1.85-2.1 kg. The corresponding solid underflowFraction 8 (51-67 kg), has a dry solids content of 5.5-6.8 kg of whichthe protein proportion amounts to only 0.9-1.18 kg.

The said solid Fraction 6 has 2 parts of water (50 kg) added and the pHis adjusted to a figure of 7 by the addition of hydrochloric acid. Theaqueous mixture is then subjected to centrifugation (liquid cyclone suchas Dorrclones). There is thus obtained a liquid overflow Fraction 9which may be discarded and a solid underflow Fraction 10 (41-46 kg)which is substantially starches with only minor amounts of protein. ThisFraction 10 has a dry solids content of 16-17 kg and the proportion ofprotein therein amounts to about 0.12-0.18 kg.

Solid Fraction 10 may then be dried in a spray type dryer to produce awhite powder material that is high in starch, approximately 97% and lowin proteins, approximately 0.1 to 0.2% and is characterized by its whitestarchy nature. The dried powder has a moisture content of approximately7% to 13%. Alternately, solid underflow Fraction 10 may be dewatered byuse of a decanter centrifuge or rotary vacuum filter to provide a dryerfeed stock in cake form rather than in slurry form. This cake form maybe dried in fluid bed type dryers or continuous belt type dryers.

The liquid overflow Fraction 3 and 7, both of which contain substantialamounts of protein, are combined and the pH of the aqueous mixture soobtained is adjusted to a figure of about 4.4. The aqueous mixture issubjected to centrifugation by use of a desludger type of centrifuge.There is thereby obtained a liquid overflow Fraction 11 (85.5-92 kg),having a dry solids content of 3.2-3.6 kg wherein the proportion ofprotein is 0.9-1.2 kg, and a solid underflow Fraction 12 (41-48 kg),having a dry solids content of 4.7-5 kg of which the protein contentamounts to 4.0-4.3 kg.

The liquid Fraction 11 contains soluble proteins together with solublesugars. It is subjected to an ultrafiltration treatment using a DorrOliver type of ultrafiltration unit having membranes with a molecularweight cut-off of about 24,000. The membranes thereby retain a certainproportion of the proteins thus allowing some additional separation ofproteins while the soluble sugars pass through the membranes. Theprotein so retained can be added to other protein fractions for furtherprocessing or spray dried separately to provide a completely solubleprotein powder.

The solid Fraction 12, containing a high concentration of proteins, isresuspended in water (24.6 kg) and the aqueous mixture so obtained istreated with hydrochloric acid in order to maintain the pH thereof toabout 4.4. The aqueous mixture is subjected to centrifugation by meansof a desludger type centrifuge. There is obtained therefrom a liquidoverflow Fraction 13 (32-38 kg), having a dry solids content of 1.4-0.55kg. of which the protein proportion amounts to 0.08-0.12 kg, and a solidunderflow Fraction 14 (28-33 kg), having a dry solids content of 4.3-4.7kg of which the protein proportion amounts to 3.9-4.2 kg. This Fraction14, which is almost completely proteins, is adjusted to a pH betweenabout 4.5 and 7.5 dried in a spray type dryer, such as a DeLaval typedryer at a low inlet temperature (about 330°-425° F.). There is thusobtained a dry powder, having a high concentration of proteins, whichhas little or no noticeable odour or flavour.

EXAMPLE 3

This example describes the wet grinding of yellow field peas to form anaqueous slurry containing dissolved proteins, sugars, solid starches andfibers and the separation therefrom of a protein powder and a starchpowder.

15 Kg of split and dehulled yellow field pea seeds (split peas: varietyCentury) in a 59.06 kg of water containing 0.94 kg of commercial gradehydrochloric acid (20° Be; 31.45% HCl) are finely ground using a Bauertype plate grinder having a setting of 0.01-0.04 inch. The aqueousslurry so obtained has a pH of about 2.5. This aqueous slurry is firstsubjected to a vibratory screening using a Sweco type screen unit toremove the bulk of the fibrous matter. There is thus obtained a liquidunderflow ("throughs") Fraction 1 and a solid overflow ("ons") Fraction2. The liquid Fraction 1 contains a dry solids content of 20-28% and theproportion of protein in that dry solids content amounts to about31-40%. The solid Fraction 2 has a dry solids content 12-25% and theprotein proportion in such dry solids content is of the other of 15-20%.

The liquid Fraction 1 is subjected to centrifugation using a decanter ordesludger type centrifuge or liquid cyclone. There is thus obtained aliquid overflow Fraction 3, having a dry solids content of 8.5-10.4% ofwhich the protein proportion amounts to 68-76%, together with a starchysolid underflow Fractions 4 having a dry solids content to 40-45% ofwhich the protein proportion amounts to about 4-6%.

The solid Fraction 2 is reslurried with 3-5 parts of water andsufficient hydrochloric acid to provide an aqueous slurry of pH 2.5.This slurry is subjected to centrifugation using a decanter type ofcentrifuge. There is thus obtained a liquid overflow Fraction 5 and asolid underflow Fraction 6. The said liquid Fraction 5 has a dry solidscontent of 5.7-8.2% and of this dry content, the protein proportionamounts to 40-55%. Liquid Fraction 5 is returned to the beginning of theprocess and serves as part of the water required for the initialgrinding of the split pea raw material. The said solid Fraction 6 has adry solids content of 25-35% containing a small proportion (5-8%) ofproteins, and is the fiber byproduct.

The said liquid Fraction 3 containing a high percentage of proteins, isfiltered as required through rotary vacuum filters or sintered metaltype filters to remove the remaining fine fibrous material. Alternatelydesludger centrifuges may be used to remove fine solid material. Thereis thereby obtained a clarified liquid Fraction 7 and a solid Fraction8.

The solid Fraction 4 containing essentially starches is subjected tosevere agitation and it is then resuspended in 3-5 parts of water andsodium hydroxide. This aqueous mixture has a pH of about 8.5 and it issubjected to centrifugation using a decanter centrifuge or liquidcyclone such as a Dorrclone. There is obtained a liquid overflowFraction 14 and a solid underflow Fraction 13. This liquid Fraction 14has a dry solids content of 4.6-7.0% and the protein proportion thereinamounts to 55-65%. The solid Fraction 13 which is substantially starcheshas a dry solids content of 25-32% and the protein proportion thereinamounts to 1.8-2.6%.

The aqueous mixture obtained by combining liquid Fraction 7 and 14 isadjusted to a pH of about 4.4 by the addition of hydrochloric acid. Thisaqueous mixture is then subjected to centrifugation using a desludgertype of centrifuge to provide a liquid overflow Fraction 10 and a solidunderflow Fraction 9. The said liquid Fraction 10 has a dry solidscontent of only 2.5-4.2% and of this, the protein proportion amounts to34-45%. The said solid Fraction 9 is rich in proteins and has a drysolids content of 13.5-16% of which the protein proportion amounts to81-87%.

The liquid Fraction 10 contains soluble proteins and soluble sugars. Itis subjected to an ultrafiltration treatment in order to separate, andthus retain, a further portion of protein from the soluble sugars.Suitable ultrafiltration equipment, such as a Dorr Oliver type machine,having membranes with a molecular weight cut-off of about 24,000, isused to retain protein on the membranes while soluble sugars remain insolution and pass through the membranes. The protein so obtained isadded to other fractions, if desired, for further processing.

The solid Fraction 9 is resuspended in water to provide an aqueousslurry having a pH of 4.4 and the pH is maintained at that figure byadding hydrochloric acid. The mixture is subjected to centrifugationusing a desludger type of centrifuge. There is thus obtained a liquidoverflow Fraction 12 and a solid underflow Fraction 1-1. The said liquidFraction 12 has a very low dry solids content of 0.25-0.8% and theproportion of protein therein amounts to 45-66%. The said solid Fraction11 has a dry solids content of 12.5-15% which is essentially proteins,the protein proportion of this solid amounting to 89-93%. This solidFraction 11 is spray dried according to the procedure described inExample 1 using a DeLaval type dryer and there is obtained a proteinpowder the same as Example 1 combined protein flows.

The solid Fraction 13 is resuspended in one part of water and theaqueous mixture thus obtained has a pH of about 7. It is subjected tocentrifugation using a Dorrclone liquid cyclone and there is obtained aliquid overflow Fraction 16 and a solid underflow Fraction 15. Thisliquid Fraction 16 has a dry solids content of 1.5-2% and the proportionof protein therein is 10-15%. The solid Fraction 15 has a dry solidscontent of 28-33% and only a minor proportion of this (0.3-0.7%) amountsto protein. This solid Fraction 15 is dried in a spray type dryer. Thereis thus obtained a dry powder which is about 98% starches on a dryweight basis containing only about 0.3-0.7% protein and is characterizedby its white starchy nature. The starch powder may contain about 7-13%of moisture.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A process for thepreparation of novel protein and starch products from legume seed whichcomprises suspending finely ground or powdered legume seed in an aqueousmedium to provide an aqueous suspension thereof wherein the pH is withinthe range of from about 2.2 to about 3.2, subjecting said aqueoussuspension to centrifugation to provide an overflow fraction containinga major proportion of soluble proteins and an underflow fractioncontaining a major proportion of insoluble starches, adjusting the pH ofsaid overflow fraction to render said proteins insoluble and isolatingsaid proteins therefrom to yield a protein product, and isolating astarch product from said underflow fraction.
 2. A process for thepreparation of a novel protein product from legume seed whichcomprises:(i) slurring finely ground or powdered legume seed in anaqueous acidic medium to provide an aqueous slurry thereof wherein thepH is within the range of from about 2.2 to about 3.2, (ii) subjectingsaid slurry to centrifugation to separate an overflow fractioncontaining said aqueous medium from an underflow fraction containingsaid slurry, and (iii) adjusting said medium to a pH of about 4.4 to 4.6to render the soluble proteins therein insoluble.